Today, type-II diabetics are continuously increasing in Japan, and the estimated number of the same exceeds 8,200,000. As a measure against this increase, interventions for preventing diabetes from developing have been made based on the glucose tolerance test, resulting, however, in unsatisfactory effects. The cause is as follows: at such a borderline stage that functional abnormalities are found by the glucose tolerance test, disorders of pancreatic islets have already advanced to a high degree, and this stage possibly is too late as a time for starting interventions.
More specifically, in the diabetes developing process, the amount of pancreatic islets (particularly, the amount of pancreatic β-cells) decreases prior to the occurrence of glucose tolerance abnormalities. Therefore, when functional abnormalities are detected or there are subjective symptoms, diabetes has already reached the stage where it is too difficult to be treated. On the other hand, if a decrease in the amount of pancreatic islets and/or the amount of pancreatic β-cells can be detected at an early stage, there is a possibility for the prevention and treatment of diabetes. Therefore, a noninvasive technique for imaging of pancreatic islets, particularly a noninvasive technique for imaging of pancreatic islets for determining the amount of the pancreatic islets and/or the amount of pancreatic β-cells, has been desired for the prevention and diagnosis of diabetes. Among these, a molecular probe that enables the imaging of pancreatic islets, preferably the pancreatic β-cell imaging, has been desired in particular.
As a molecular probe for imaging pancreatic islets in a sliced section, exendin(9-39) is known, which is one of ligands of GLP-1R (glucagon-like peptide-1 receptor). More specifically, it is known that 125I labeled exendin(9-39) is administered to mice by intravenous injection through the tail vein, 125I labeled exendin(9-39) accumulates selectively and specifically in the pancreas among organs, and binds selectively to pancreatic islets in the pancreas (E. Mukai et al. Non-invasive imaging of pancreatic islets targeting glucagon-like peptide-1 receptors, 44thEASD Annual Meeting Rome 2008, abstract, Presentation No. 359 [on line] (Document 1)).